Circuit breakers are commonly used for providing automatic circuit interruption upon detection of undesired overcurrent conditions on the circuit being monitored. These overcurrent conditions include, among others, overload conditions, ground faults and short-circuit conditions.
Circuit breakers typically include an electrical contact on a movable arm which rotates away from a stationary contact in order to interrupt the current path. The type of overcurrent condition dictates how quickly the arm must rotate. For example, in response to overcurrent conditions at relatively low magnitudes but present for a long period of time, circuit breakers generally move the arm to break the current path by tripping a spring-biased latch mechanism which forces the contact on the arm away from the fixed contact. Spring-biased latch mechanisms are usually relatively slow. In response to overcurrent conditions at relatively high magnitudes, circuit breakers must break (or blow-open) the current path very quickly, reacting much faster than the reaction time for known spring-biased latch mechanisms. In either case, the contact arm must rotate to an open position as fast, as simply and as reliably as possible.
Circuit breaker designs attempting to achieve these objectives of quickness and reliability have failed. For example, most circuit-breaker blade suspension mechanisms require complex manual assembly involving high part count, intricate positioning of one or more drive pins and one or more torsion springs for biasing movable arms, and their overall intricate assembly prohibits late point assembly adjustments, field adjustment and/or service. In addition, the complex design of most circuit-breaker blade suspension mechanisms is not conducive to straight-pull molding techniques during manufacturing.
Many conventional circuit-breaker blade suspension mechanisms also exhibit problems in terms of their operation. These problems include slow contact arm rotation, the contact arm rebounding to the closed-contact position during interruption, breakage of the crossbar used to support the contact arm, and inconsistent contact force characteristics.
Generally, the speed and reliability at which the blade suspension mechanism breaks the current path is directly related to the complexity of the blade suspension mechanism, i.e., the faster the mechanism and the higher its reliability, the more complex the mechanism.
Accordingly, there is a need for a blade suspension assembly for a circuit breaker which overcomes the above-mentioned deficiencies of the prior art.